What Size Generator Do You Need for a Sump Pump?
Quick answer
To run a sump pump (1/3 hp) alone, a generator needs at least 800 running watts and 1,600 starting watts. A 1/3 hp sump pump draws about 800 running watts and roughly 1,600 starting watts. A 1/2 hp unit runs about 1,050 W with a surge near 2,100 W. These are typical values for residential pedestal and submersible pumps.
Running it on a portable
Portable generators in our dataset that clear both numbers on their own:
| Model | Running watts | Starting watts | Approx. price |
|---|---|---|---|
| Honda EU2200i | 1,800 | 2,200 | Around $1,150 |
| WEN 56235i | 1,900 | 2,350 | Around $450 |
| Westinghouse iGen4500 | 3,700 | 4,500 | Around $899 |
| Champion 4500W Dual Fuel Inverter (200989) | 3,500 | 4,500 | Around $999 |
| Firman P03631 | 3,650 | 4,550 | Around $800 |
| DuroMax XP13000EH | 10,500 | 13,000 | Around $1,299 |
Running it in a whole-home system
In a whole-home outage load list - the sump pump (1/3 hp) plus about 3,225 W of household essentials - the combined math lands in the 13 kW standby class with standard headroom. Standby units in that class from our dataset:
| Model | Output | Approx. unit price | Warranty |
|---|---|---|---|
| Cummins QuietConnect 13kW (RS13A) | 13 kW | Around $4,300 | 5-year |
The sump pump is small but non-negotiable: it runs hardest during the storms that cause outages, and a flooded finished basement costs more than any generator on this page. Because the load is small, this is the one pump a mid-size portable or even a large battery station genuinely covers - as long as the unit can supply the 1,600 W starting surge.
A note on climate
The math above assumes a mixed climate. Two adjustments matter at the extremes, and both are rules of thumb, not measurements. In a cold climate, heating dominates: the furnace blower runs near-continuously, and if the house has a heat pump with electric auxiliary heat strips (typically 5-15 kW), those strips are the single biggest sizing load in the house when they engage - count them at full draw or use load management to shed them. In a hot climate, the air conditioner is the dominant load and runs near-continuously through a heat-wave outage, so installers commonly add roughly 10% extra headroom on top of the standard margin. Our generator size calculator applies both adjustments openly - you can see exactly what changed.
FAQ
What happens if the generator is too small for the surge?
The voltage sags when the motor tries to start. Motors hum, overheat, or fail to start; electronics on the same circuit may reset; the generator's breaker may trip. Repeated failed starts are hard on both the motor and the generator - undersizing is the expensive kind of cheap.
Do I need to count this load if I have load management?
Load management lets a smaller generator carry a bigger list by shedding selected loads in priority order. It works well for deferrable loads (water heater, dryer, EV charger) and poorly for loads you truly need the moment they call (a sump pump during a storm).